As is known, bridge cranes are machines destined to lift and displace materials and goods, in both external and internal environments, and are generally constituted by a bridge mobile in a horizontal direction along a pair of rails and provided with a cross member on which a carriage is mounted, the carriage housing a hoist that can move horizontally along the cross-member. A winch is connected to the hoist, the winch having a gripping element, for example a hook, for gripping and raising objects.
The winch has one or more cables applied to it, which via a system of hoists, relays and hooks enables lifting and displacing weights.
One of the main problems connected to the use of these plants, as well as in general relating to cable or chain lifting apparatus, is to guarantee the full safety of the operators during the use thereof, also in consideration of the large weights to be moved.
A solution to these problems has been provided by the device described in Italian patents IT 1 386 901 and IT 1 387 564, to which reference is made for further details.
The safety device for lifting apparatus described herein include means for detecting a displacement from the vertical of at least one of the cables which support the gripping element for the load.
An embodiment includes the use of a group of accelerometers, each of the accelerometers being able to determine displacement of the load gripping element on a respective orthogonal Cartesian axis.
In particular, the accelerometers are positioned on the fixed head of the cable, i.e. at the point where the cable supporting the gripping element of the load is fixed and dos not move, i.e. does not slide.
To the detecting means of the displacement from the vertical, acoustic and/or visible warning means, or stop means of the lifting or displacing operations can be associated and able to enter into function if the displacement from the vertical of the cable exceeds at least a predetermined threshold.
A further solution is described in Italian patent IT 1 393 950, to which reference is made for further details.
Briefly, the above document relates to a system enabling integrated management of lifting plants, which system is indicated as Cranes Integrated Management Services (CIMS).
The system enables detecting and cataloguing the data relating to the components of a lifting plant, with the aim of increasing security thereof, for example in order to be able to manage maintenance operations in a way that is clear and simple for the clients.
For example, by means of an accelerometer detecting system located on-board the lifting apparatus data relating to the displacements of the load gripping element, data relating to the displacements of the gripping element of the load on at least an orthogonal Cartesian axis and/or data relating to single events or historical series of events of the lifting apparatus can be detected.
The system enables, among other things, increasing efficiency in managing the maintenance, especially in all those industrial situations where a multiplicity of plants is present.
The data collected can be made available directly on the web without the use of programs installed on the PC, which enables maximum overall accessibility from any Internet station.
However, notwithstanding the fact that the bridge crane is a lifting apparatus subject to specific norms both constructional and relating to periodic checks, the following technical problems remain open, substantially linked to the safety of operators using the apparatus.
One of these problems is given by the fact that the devices of the prior art, though able to determine the displacement of the load with respect to the vertical, perform the determination substantially with the aim of enabling the operator to take the appropriate decisions in a case of excessive displacement. However they do not operate actively to minimize or in any case reduce the swinging of the load during the operations of the bridge crane.
Likewise, though there exist theoretical studies that deal with the problems relating to the swinging of the load in lifting apparatus, the studies are generally based on simulations or laboratory prototypes and generally do not take account of the needs that arise in the industrial field, for example due to the presence of the operator and the commands sent thereby, in respect of the norms and other elements.
A further known device is described in document US 2005/103738, which describes several embodiments of a control system for the swing of a load.
In an exemplary embodiment of such known control system, two inertial platforms are provided.
The first inertial platform is coupled to measure an acceleration of a first object, such as a load, suspended from a second object, such as a trolley, the first inertial platform generating a first signal representing the acceleration of the first object.
The second inertial platform is coupled to measure an acceleration of the second object, the second inertial platform generating a second signal representing the acceleration of the second object.
The device of US 2005/103738 further comprises a processor in communication with the first and the second inertial platform, the processor operable to determine a sway of the first object with respect to the second object based at least in part on the first and second signals, the sway representing a relative displacement of the first object with respect to the second object.